Make app.get/app.set available in browser

Implement settings object and methods in browser-express.

This is a back-port of #299 minus the tests, because the 1.x branch does not have `describeOnServer` helpers required to run `app.test.js` in the browser.

/to @ritch or @raymondfeng: please review.

This patch is needed to make loopback 1.x compatible with loopback-boot running in a browser, loopback-boot 2.0 and the new project layout.